It is known to package objects in a thermoplastic and heat-shrinkable synthetic-resin sheet or foil in an automatic machine to which is delivered a succession of objects to be packaged as well as a continuous supply of the wrapping web and which produces at its output a succession of discrete individually wrapped packages. The wrapping web is typically fed as a single sheet or foil from a supply roll to the machine. In the machine its two longitudinal edges are folded over and welded together automatically to form a tube into which the succession of objects is fed. Transverse sealing bars are provided which form transversely extending seals between the two sides of the tube in front of and in back of each object to be wrapped, and a blade normally connected to the welding tools serves to sever off the packaged and sealed-in object.
In order to form these transverse seams in a continuously operating process it is necessary either to stop the advance of the object as the transverse seams are formed, or to move the welding tools along with the object for the welding operation. In this latter arrangement it is necessary to feed the objects in, regardless of their lengths, at predetermined intervals so that the synchronizing equipment for displacement of the welding tools along with the moving objects can be made as simple as possible. Even in such an arrangement, however, the system remains rather complex and trouble-prone, and when relatively short objects are being packaged considerable quantities of the wrapping web are wasted. Furthermore in such arrangements the foil normally used as a wrapping web typically wrinkles up on the objects and presents an unattractive appearance.
Other systems allow more adjustment for package length, but in each case the welding time therefore becomes a function of conveying speed and package length. Thus some of the seams will be inadequately strong because of a too short welding time and others might be melted completely through due to a too long welding time.
U.S. Pat. No. 3,473,288 has suggested a system wherein the objects, once inside the tube, are advanced between upper and lower belts which vertically pinch the entire package and tube together. Such an arrangement has the disadvantage, however, that an exact positioning of the objects during the welding operation is still not ensured. Thus occasionally the welding tools will close down on the object itself, or at a relatively long distance from the object making the package loose and unattractive. This is normally compensated for by providing a relatively large gap between packages so that even though some of the wrapping web is wasted the seam is sure to fall in an empty area between adjacent objects.
Other solutions have been suggested such as in German Pat. No. 338,600 and in German Patent Publication No. 1,800,988. None of these arrangements is capable of adjusting to objects of different lengths and heights, so as to form a succession of snug and neat packages without substantial waste of the wrapping web.